1. Field of the Invention
The present invention relates generally to braided structures characterized by three over, three under braid pattern rather than the prior art conventional two over, two under braid pattern and to methods and apparatus for producing three over, three under tubular braided products.
More specifically, the invention is directed to a tubular braided structure that is especially suited for use as an improved reinforcement for tubular conduits such as hose.
The invention further is directed to a method and apparatus for producing three over, three under tubular braid structures utilizing a Maypole type braider.
2. Description of the Prior Art
Braided structures have long been used to provide a combination of strength and flexibility to products such as rope and cable formed of yarn or wires as well as to provide reinforcement for flexible tubular structures or conduits, for example to reinforce hose for high pressure service by applying a braided yarn or wire reinforcing sleeve thereto.
For the last fifty or more years, braided reinforcement for flexible tube-like conduits such as hose has utilized a "two over, two under" braid configuration and virtually all apparatus for forming such structures has been built to produce a two over, two under hose reinforcing braids.
The methods employed and the apparatus utilized in producing a conventional two over, two under braid vary to some degree, but fall basically in two categories. The first is the so-called Maypole or sinuous braiding technique wherein the strand carriers are moved in intersecting serpentine paths on a braiding deck as the strands are let off under tension onto the tubular structure to be reinforced which is pulled at a uniform rate in a direction perpendicular to the deck. Although early forms of Maypole braiders utilized various mechanisms for driving the carriers in opposite directions around sinuous tracks mounted on the braider deck, modern Maypole braiders utilize planetary gearing and a cam track and cam follower system on the carriers and drivers to eliminate the sinuous tracks and their attendant high friction and wear problems. An example of such a modern planetary gear type Maypole braider is shown for example in my U.S. Pat. No. 3,783,736, issued Jan. 8, 1974 and foreign counterparts thereof, to wit:--Canadian Reg. No. 986342, filed Mar. 30, 1976; French Reg. No. 2196651, filed Mar. 4, 1974; German Reg. No. 2341144.1, filed Apr. 3, 1986; British Reg. No. 1393836, filed Aug. 7, 1973; Italian Reg. No. 992953, filed Sep. 30, 1975; Japanese Reg. No. 12192919, filed on Jul. 26, 1984; and Mexican Reg. No. 140433, filed on Oct. 24, 1979.
In a second type of braiding technique, the strand carriers are arranged in two annular groups which are axially spaced with respect to the tube to be reinforced. The groups are rotated in opposite directions with respect to the tube and a mechanism is provided for alternately guiding the strands from the outer group of carriers over and under the carriers of the inner group. Apparatus for carrying out this second technique is known as a rotary braider, an example of which is disclosed in U.S. Pat. No. 4,034,642 issued Jul. 12, 1977.
Although the rotary braider could conceivably be modified to produce a three over, three under braid, such modification would result in greatly increased machine complexity and cost, and decreased productivity. In contrast, the utilization of a Maypole braider actually simplifies the machine and reduces its cost, while significantly increasing productivity.
All tubular braid structures are comprised of at least two strands which are wound in oppositely directed helical paths that pass over and under one another in a prescribed sequential interval. Usually, each strand is a composite structure composed of a plurality of individual flexible elements (such as yarn or wire) aligned to form a flat ribbon-like strand of individual parallel but unconnected elements. However, in some braid structures the strand elements can be bunched and/or twisted. When a composite strand (without regard to whether it is flat, bunched or twisted) is braided in an over and under pattern, equal lengths of the individual elements of a given strand are drawn from a carrier reel or bobbin and forced to travel different paths and thus different distances. Thus, producing a tubular braid structure from such composite strands requires a non-linear supply of strand elements from a linear supply source and this creates tension in some elements and slackness in others. This constantly changing condition occurs to some degree in any tubular braid and is influenced by the pattern interval of over and under plaiting, and by the density or percent of strand coverage involved and by the stiffness of the strand elements.
Usually, the strand element length differences are not so great that they cannot be handled to some degree in one of two ways.
First, the carrier let-off on the braider is always a tension release device insuring that the composite ribbon-like strands are payed-off to the braid structure under sufficient tension to elastically stretch only the shortest of the individual strand elements, therefore enabling each strand to be braided into the fabric. Without such tension, the deviation of length demand results in a few taut strand elements and others becoming slack and producing an unforgiving entanglement of strand elements.
Secondly, the strand supply bobbins can exist with the intrinsic non uniform linear demand, because during braiding the individual strand elements are able to adjust their relative positions within a given strand in an attempt to compensate for the length differentials between the elements of the strand and such repositioning results in "crossovers" and can be seen in the shift of strand wire 15 in FIGS. 11b and 11c.
Although these problems occur in all braid of a tubular type, neither strand tensioning during pay off nor strand element realignment provides a total solution. This is because the differing lengths and differing tensions under which the strand elements are braided into the structure precludes the strand elements from being able to share equally when under load and stress activity. However, the three over three under pattern of this invention has a discernably different and more graceful flow that involves fewer directional changes. This reduces strand element length deviations to but a small fraction of that experienced in the harsher two over, two under structure of conventional braids. In the great majority of braid constructions, "crossovers" will be substantially, if not totally, eliminated with the three over, three under braid pattern. A crossover is a misaligned element in a strand and is illustrated in FIG. 11b.
The reinforced hose industry has been constantly seeking to increase the performance of conventional two over, two under reinforcements to permit the hose to be used under higher operating impulse pressures, to have longer cycle life, to operate at higher working temperatures and to have increased flexibility. These efforts generally have focused variously on the use of stronger reinforcing materials, improved conduit materials, increased utilization of the available strand space (i.e., strand "coverage" or strand density), twisting of the strand elements, pressurized treatment of the braid structure prior to use and combinations of such modifications. However, the dynamics of this system is such that enhancement of one characteristic usually has an adverse effect on other characteristics.
To illustrate, the conventional two over, two under braided reinforced hose comprises a plurality of flat strand elements of parallel yarns or wires, the wire being typically employed for high pressure hose. Since the impulse strength of reinforced hose is essentially dependent upon the amount of material in the braided reinforcement, improved hose strength is achieved by utilization of a plurality of braided layers. Such an approach is expensive in that a second braiding operation is required, and a second braided reinforcement overlay does not effectively serve to double the hose burst strength; it decreases flexibility and adds to the weight and cost of the hose.
The strength of reinforced hose is also a function of the tensile strength of the reinforcing material used. However, it has been found that the two over, two under reinforcing braids cannot be made with wires having a tensile strength much above about 350,000 p.s.i., primarily because wires having higher tensile strengths tend to be more brittle and cannot easily accommodate the severe and abrupt directional changes imposed by the two over, two under braid pattern.
Further, to maximize strand coverage of the reinforcement with conventional two over, two under braid pattern, the braiding must be carried out with the braid strand being under very high tension and to do so usually requires the hose itself must be rigidified by chilling and/or supported internally during the braiding so as to prevent its deformation and extrusion between the strand elements. Rigidification and internal support are also desirably used in producing the three over, three under braid pattern of this invention.
A significant departure from the conventional flat braid comprised of carefully controlled parallel wires is disclosed in the Slade U.S. Pat. No. 3,463,197, wherein a mounded strand configuration utilizing a large number of small wires was proposed in the two over, two under braid pattern. This "high pack" approach, because of its increased wire content and coverage provided, markedly improved hose performance, especially in terms of impulse strength and has been widely used despite its increased cost in high pressure hose applications. However, when the Slade configuration is used in conjunction with the three over, three under braid pattern the performance characteristics are still further enhanced in that the same strength levels can be obtained with less yarn or wire, thereby lowering the cost and the resulting hose has greater flexibility at comparable strength levels.
U.S. Pat. No. 4,567,917 to Millard adds a further step to the mounded configuration proposed by Slade, namely the preforming of the wire and the twisting of the strand elements in an attempt to more equally distribute the pressure loads on the strand wires, but again this utilized in a two over/two under braid pattern. However, twisting the stranded elements necessitates an additional operation and increases the cost, whereas comparable performance levels can be obtained with a simple three over, three under pattern at less cost.
Thus, despite the proposed changes in configuration of the strands and the materials and number of ends comprising each strand, a constant characteristic of braided reinforced hose over the past fifty years has been the utilization of the standard two over, two under braid pattern.
Unfortunately, the geometry of the two over, two under braid pattern is such that constraints are imposed not only on the selection of materials that can be used but also on the braiding operation itself. Therefore, further improvement in the production of reinforced hose and its performance of a substantial nature cannot be anticipated with presently available materials, braiding apparatus and braiding techniques.
The reinforcing braid proposed by the present invention departs markedly from the accepted two over, two under pattern standard.